The term “noncoordinating anion” is now accepted terminology in the field of olefin and vinyl monomer polymerization, both by coordination or insertion polymerization and carbocationic polymerization. See, for example. EP 0 277 003, EP 0 277 004, U.S. Pats. Nos. 5,198,401, 5,278,119, Baird, Michael C., et al, J. Am. Chem. Soc. 1994, 116, 6435-6436, U.S. Pat. Nos. 5,312,881, 5,502,017, 5,668,234, and WO 98/03558. The noncoordinating anions are described to function as electronic stabilizing cocatalysts, or counterions, for essentially cationic metallocene complexes which are active for polymerization. The term noncoordinating anion as used here applies both to truly noncoordinating anions and coordinating anions that are at most weakly coordinated to the cationic complex so as to be labile to replacement by olefinically or acetylenically unsaturated monomers at the insertion site. These noncoordinating anions can be effectively introduced into a polymerization medium, or premixed with an organometallic catalyst compound prior to introduction into the polymerization medium, as Bronsted acid salts containing charge-balancing countercations, ionic cocatalyst compounds. See also, the review articles by S. H. Strauss, “The Search for Larger and More Weakly Coordinating Anions”, Chem. Rev., 93, 927-942 (1993) and C. A. Reed, “Carboranes: A New Class of Weakly Coordinating Anions for Strong Electrophiles, Oxidants and Superacids”, Acc. Chem. Res., 31, 133-139 (1998).
Both of U.S. Pat. No. 5,198,401 and WO 97/35893 specifically address nitrogen-containing Bronsted acid cations capable of donating a proton, to suitable Lewis acidic organometallic catalyst compounds, as part of ionic cocatalyst compounds that in turn are capable of activating said organometallic compounds by rendering them cationic and providing a compatible, counterbalancing noncoordinating anion. U.S. Pat. No. 5,198,401 describes catalyst activator compounds represented by the formula [(L′-H)+]d[(M′)m+Q1Q2 . . . Qn]d− where L′ is a neutral base, H is a hydrogen atom and [(M′)m+Q1Q2 . . . Qn] is a metal or metalloid atom subtended by a variety of ligands, preferably where M is boron and two or more of Qn are aromatic radicals, such as phenyl, napthyl and anthracenyl, each preferably fluorinated. L′ is illustrated with various trialkyl-substituted ammonium complexes and N,N-dialkylanilinium complexes. WO 97/35893 describes cocatalyst activator compounds represented by the formula [L*-H]+[BQ′4]− where L* includes nitrogen containing neutral Lewis bases, B is boron in an oxidation state of 3, and Q′ is a fluorinated C1-20 hydrocarbyl group, preferably a fluorinated aryl group. The cocatalyst compounds are said to be rendered soluble in aliphatic solvents by incorporation of olephilic groups, such as long chain alkyl or substituted-alkyl groups, into the Bronsted acid L*. Bis(hydrogenated-tallowalkyl)methylammonium and di(dicosyl)methyl-ammonium salts are exemplified.
EP 0 426 637 describes the use of the cocatalyst compound non-substituted triphenylcarbenium tetrakis(pentafluorophenyl)boronate as a proton-free ionizing agent that abstracts a metal ligand to form a catalytically active metallocene cation and a loosely coordinated anion. U.S. Pat. No. 5,502,017 addresses ionic metallocene catalysts for olefin polymerization comprising, as a cocatalyst component, a weakly coordinating anion comprising boron substituted with halogenated aryl substituents preferably containing silylalkyl substitution, such as para-silyl-t-butyldimethyl. This substitution is said to increase the solubility and thermal stability of the resulting metallocene salts. Examples 3-5 describe the synthesis and polymerization use of the cocatalyst compound triphenylcarbenium tetrakis (4-dimethyl-t-butylsilyl-2, 3, 5, 6-tetrafluorophenyl)borate.
Olefin solution polymerization processes are generally conducted in aliphatic solvents that serve both to maintain reaction medium temperature profiles and solvate the polymer products prepared. However, aryl-group containing activators, such as those having phenyl derivatives and other fused or pendant aryl-group substituents, are at best sparingly soluble in such solvents and typically are introduced in aryl solvents such as toluene. Solution polymerization processes in aliphatic solvents thus can be contaminated with toluene that must be removed to maintain process efficiencies and to accommodate health-related concerns for both industrial manufacturing processes and polymer products from them. Alternatively, relatively insoluble catalyst components can be introduced via slurry methods, but such methods required specialized handling and pumping procedures that complicate and add significant costs to industrial scale plant design and operation. Low solubility can also become disadvantageous should the process involve low temperature operation at some stage such as in typical adiabatic processes run in areas subject to low ambient temperatures. Additionally, separating or counteracting the build up in the recycle system of aromatic catalyst solvents may become another problem. At the same time means of maintaining high molecular weights in olefin polymers while operating at economically preferable high polymerization reaction temperatures and high polymer production rates is highly desirable. It is therefore desirable to identify olefin polymerization cocatalyst activators which are active for polymerization, particularly at elevated temperatures, which are more soluble in aliphatic solvents.